A reconfigurable CMOS mixer for SDR or multi-standards is designed and implemented using 0.25um CMOS process. To realize this mixer, a flexible input matching network consisted of inductor and capacitor bank is suggested, which is a kind of variable reactance transformer. This network controls input impedance of the mixer and matches that to source impedance according to operation frequency.
The designed mixer core is double-balanced Gilbert cell structure and connected to 2 flexible matching networks differentially. Simulation result shows good return loss below -10 dB and acceptable performance in wide frequency band off ~ 6 GHz. Based on the results of the mixer performance, the mixer is applied to present commercial standard such as WCDMA, 802.11a/b/g and simulation results are presented correspond to each standard characteristic, especially bandwidth.
By using proposed method, a reconfigurable CMOS mixer is implemented and measured. In WCDMA application, the specific measured parameters of the mixer are the conversion gain of 9.5 dB, NF of 13.8 dB, and IIP3 of -2.6 dBm. In IEEE 802.11b/g application, those are the conversion gain of 8.3 dB, NF of 12.1 dB, and IIP3 of -1.9 dBm. In IEEE 802.11a application, those are the conversion gain of 6.2 dB, NF of 14.8 dB, and IIP3 of -1.1 dBm. These values meet most of simulation specification except conversion gain due to the power consumption of the matching network.
In brief, we can obtain a reconfigurable mixer with wide range of input impedance matching capability from 2 GHz to 6 GHz using flexible input matching method. It supports not only WCDMA, 802.11a/b/g frequency bands but also unlicensed frequency band between 2 and 6 GHz, so it can be used to multi-standard or SDR applications.